Three-dimensional morphology of rigid structures as a tool for taxonomic studies of Dactylogyridae (Monogenea).

María A Rossin,Pablo N De Francesco,Juan T Timi

doi:10.1007/s00436-017-5591-y

Abstract

Dactylogyridae is overwhelmingly the most abundant and diverse taxon among monogeneans in continental waters of South America. Their small body size requires considerable sampling effort and training for collecting and identifying the worms from the gills, skin, nasal cavities, and other microhabitats. Indeed, diagnostic characteristics as sclerites and male copulatory complex are generally less than 100-μm long and are essential for taxonomic description and identification of species. Here, a combination of simple and routine methods for three-dimensional morphological studies on hard structures is proposed for dactylogirids: SDS treatment for clarification of specimens and enzymatic digestion with proteinase K for freeing sclerotized structures, followed by laser confocal microscopy. This method is applicable to fresh or fixed specimens and does not require staining or dehydration. Indeed, stable autofluorescence emission is detectable at 500-530nm for bars, anchors, and male copulatory complex when excited by argon laser. Advantages of this protocol over previous methodologies for taking laser confocal images are discussed. Open access software for image processing was used for three-dimensional reconstruction of sclerotized structures generating models and full 360° rotation videos.

Highlights

Monogeneans are a diverse group in terms of species richness, being highly variable in their morphology and ecology (Poulin 2002)
While alcohol-fixed specimens are digested in a few minutes (Fig. 1e, f), the formalin-fixed specimens should be previously washed in distilled water to achieve total digestion with proteinase K, in this case, the process can take from a few minutes to hours
Its application to the study of rigid structures of monogeneans represents an important advance for the systematics of this taxon (Galli et al 2006, 2007; Garcia-Vásquez et al 2012), supposes that the application of tedious protocols and desirable results is not always achieved

Summary

Introduction

Monogeneans are a diverse group in terms of species richness, being highly variable in their morphology and ecology (Poulin 2002). Despite the efforts made by taxonomists, it is estimated that only less than 3% of the monogeneans parasitizing freshwater fishes are known in this region (Thatcher 2006). This fact can be a consequence of their small body size (< 1 mm), which requires a higher sampling effort and considerable training for collecting and identifying the worms from the gills, skin, nasal cavities, and other microhabitats. The scarce numbers of taxonomists in the field, the complex morphology of dactylogyrids, and their confusing classification have led to many incorrect or erroneous taxonomic determinations

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